Carbon-based materials are considered as having a great potential to improve digital and radio frequency (RF) electronics. Graphene is a name given to a single layer of carbon atoms arranged in a honeycomb lattice, although also films built of few graphene sheets stacked one upon another are often referred to as graphene (or few-layer graphene) and shall also be considered as embodiments of a graphene layer herein. Single-layer graphene is a zero band gap semiconductor with outstanding material properties, such as charge carrier mobility of around 1.2×105 cm2/Vs at 240 K, high field electron velocity of 4×107 cm/s, sheet resistance as low as 125 Ω/sq (about 30 Ω/sq for four-layer films), and thickness of only 0.34 nm.
Most of the work on graphene devices has been so far devoted to field-effect transistors with graphene channel (GFETs). These transistors use single-layer graphene, because field effect in thicker films is hampered by screening, which strongly reduces the transconductance.
Although the realization of a logic switch based on GFET is hindered by the lack of band gap in graphene, this material may have a great potential for RF applications. This field of graphene research has recently attracted a great interest of physicist and device engineering community and resulted in realization of RF graphene field effect transistors (GFET) with cut off frequency (fT) of 100 GHz, ambipolar graphene RF mixers, and graphene frequency multipliers. A high-performance RF (radio frequency) junction transistor is known from WO 2010/072590. Control of operation of such a transistor is performed by driving a tunnel junction, which allows a flow of electrons in one direction when subjected to an operation voltage.